Open Ceramics最新文献

This study examines the photocatalytic activity of the green synthesized (using lemon juice) MgO nanoparticles under a halogen light for the degradation of Congo Red (CR). The characterization of the prepared sample was studied by applying Fourier Transform Infrared (FTIR) Spectroscopy, X-ray Diffraction (XRD), Scanning Electron Microscopy (SEM), and Thermogravimetric Analysis (TGA). By applying XRD analysis, the crystallographic variables of the MgO NPs were determined and the crystallite size was obtained from a variety of formulas/models (Scherrer equation, Williamson-Hall model, Monshi-Scherrer model, Size-Strain Plot, Halder-Wagner model, etc). The crystallite size was found in a valid range of 4.62–99.03 nm. Photocatalytic degradation of Congo Red (CR) has been made under halogen light by considering a dye concentration of 20 ppm at 40 mL solution for 0.05 g of the catalyst sample. Operating conditions were fixed as neutral pH, 25 °C temperature, and 40 min exposure time of the halogen lamp.

In barium titanate (BaTiO₃) the relative permittivity varies as a function of grain size due to the influence of various sizes and scaling effects. The cold sintering process (CSP) has been applied to sinter nanocrystalline BaTiO₃ (<200 nm), however in conventionally sintered BaTiO₃ a maximum relative permittivity is achieved at average grain sizes around 0.8 μm. In this work the feasibility of cold sintering 1 μm BaTiO₃ inclusions in ratios of fine-grained BaTiO₃ matrixes from 50 to 200 nm is investigated. Occurrences of both conformal sintering of inclusions into the matrix and constrained sintering with residual porosity are observed. Subsequently, electrical resistivities increased from 1 × 10⁸ Ω cm to approximately 1 × 10¹² Ω cm by a post CSP heat treatment of 500 °C. Relative permittivity of annealed samples increases systematically following a logarithmic mixing law as a function of matrix grain size and increasing the ratio of inclusions to matrix.

This work proposes an effective methodology for measuring the porosity of mixed hydraulic binders applying image analysis (IA) with confocal microscopy (CM). CM offers a certain simplification of sample preparation compared to the standard procedure EN 480-11, as the steps of sample staining and pore masking are eliminated. A set of cement and a hydraulic clinker-free sulfocalcic binder pastes was prepared with various aeration. Total air content, micro air content and the air pore spacing factor according to EN 480-11 standard were determined for hardened pastes using measuring chords. Subsequently, a new simple Surface porosity evaluation for IA methodology using CM was proposed and results were compared with the standard evaluation. The results of both IA evaluations achieved high agreement and the new porosity Surface evaluation was found to be promising for the determination of total air content. Porosity values measured by both IA methods were further compared with MIP.

High-entropy ceramic-based cermets represent a new and promising direction in improving the mechanical properties of conventional hardmetals through the formation of complex microstructures during synthesis. This has been systematically studied in two Co-free, high-entropy (Ti,Zr,Hf,Nb,Ta)C ceramic-based cermets using 10 wt% Ni and 10 wt% FeCrAl metallic binders during hot-press and spark plasma sintering. Fully densified microstructures were achieved in the temperature range of 1400–1500 °C, which is below the melting points of the pure Ni and FeCrAl alloy, owing to the liquid-phase assisted sintering. The optimal densification routes resulted in Vickers hardness (HV₃₀) of 16.77 ± 0.72 and 18.32 ± 0.99 GPa, and fracture toughness (K_{Ic_SENB}) of 5.31 ± 0.41 and 4.83 ± 0.50 MPa m^0.5, respectively for the Ni and FeCrAl bonded cermets. The improved damage tolerance of these cermets compared to the base (Ti,Zr,Hf,Nb,Ta)C high-entropy carbide is related to the reduced grain size and microstructural toughening mechanisms (e.g. crack deflection and bridging).

The Meiganga lateritic clays and termite mounds were characterized for their use as construction materials. The six collected samples were subjected to mineralogical, geochemical, and physico-mechanical tests. Quartz, kaolinite, hematite, goethite, gibbsite, muscovite, and anatase are the main minerals in raw materials, while after firing at 1050 °C, mullite is formed. The SiO₂/Al₂O₃ ratio greater than 1 indicates a high SiO₂ content, which is consistent with the presence of quartz as an associate mineral to kaolinite. Considering linear shrinkage globally less than 5 % and flexural and compressive strengths greater than 2 and 7 MPa, respectively, four clay materials are suitable to produce bricks at all the studied temperatures, whereas two others only after firing at 1050 °C. As the studied characteristics do not depend on the nature of the material, exploring termite mound material in the Meiganga area would provide additional good-quality material to make up for any deficit that might arise.

An improved understanding of the oxidation resistance of HfC-TaC ultra-high temperature ceramics (UHTCs) is developed through modeling of the phase equilibria in the Hf-Ta-O system and HfO₂-Ta₂O₅ isoplethal section. CALculation of PHAse Diagrams (CALPHAD) thermodynamic models of the systems are developed in conjunction with experimental data from the literature and first-principles calculations. Density functional theory (DFT) calculations accurately describe thermodynamic properties of binary oxides in the Hf-Ta-O system and predict cation disorder in Hf_(n-5)/2Ta₂O_n. The ternary modeling includes revised models of the Hf–O system and existing models of the Ta–O and Hf–Ta systems. The Hf_(n-5)/2Ta₂O_n ternary oxide series is modeled as three entropically stabilized solid solutions with disordered cation sublattices that increase in stability with structure size. Hf₄Ta₂O₁₃ is considered a metastable phase based on the present models and phase diagram, consistent with the lack of experimental data supporting its stability. The calculated phase diagrams improve upon prior ones and predict optimal thermal resistance of HfC-TaC ceramics at compositions between 3HfC-1TaC and 4HfC-1TaC.

Geopolymers are a type of inorganic substance that is created in an alkaline environment using alumina-silica gel. Although extensive research has been conducted on geopolymer concrete's mechanical and durability properties, its practical usage is limited by the constraints of attaining optimal curing conditions and the demand for high-temperature curing. These factors make it challenging to use geopolymer concrete in on-site construction projects. The current study aimed to explore the feasibility of substituting fly ash (FA) with sugarcane bagasse ash (SCBA) in geopolymer concrete (GPC) cured at ambient temperature, as a means of resolving this problem. SCBA was utilized as a partial replacement for FA, ranging from 5 % to 20 %. Various tests, including slump test, compressive strength (C_st) test, tensile strength (S_st) test, and flexure (F_st) tests, were performed. Scanning electron microscopy (SEM) and X-ray diffraction (XRD) analysis were used to study the microstructure. Furthermore, the effect of various curing temperatures was investigated. The results show that substituting SCBA for FA can reduce the necessity of curing at high temperatures. Furthermore, following a 28-day period of curing at ambient temperature, the geopolymer concrete mixtures made with FA-SCBA exhibited compressive strengths ranging from 40 to 56 MPa. These results imply that SCBA could be a suitable substitute for FA in GPC applications, reducing energy usage and environmental effects.

Robocasting stands as a pertinent additive manufacturing technique for producing intricate ceramic parts. Amidst stricter environmental regulations, the adoption of natural additives becomes imperative. This study investigates the influence of plant-based additives on the rheology and printability of eco-friendly pastes.

Various 50 vol%-alumina pastes were formulated using natural binders, plasticizers and dispersants (e.g., lignosulfonate, polysaccharides, glycerol) and then assessed through oscillation and flow rheological analyses. Paste viscosity and rigidity often deviated from printability maps reported in the literature, showing the complexity of defining universal printability criteria. A comprehensive investigation was conducted on the water retention capabilities of additives, liquid phase migration and paste drying kinetics.

This paper highlights the critical importance of constraining liquid phase migration within eco-friendly ceramic pastes and the crucial role of polymer chain reorientation under shear. Consequently, this research lays diversifying formulations, offering sustainable solutions for industrial ceramic applications.

The use of additive manufacturing (AM) processes has grown rapidly over the last ten years like fused deposition modelling and stereolithography techniques. 3D printing offers advantages in ceramic component production due to its flexibility. To enhance quality and reduce resource consumption in ceramics industry, fast, integrated, sub-surface and non-destructive inspection (NDI) with high resolution is needed. This study demonstrates sub-surface monitoring of 3D printed alumina parts to a depth of ∼0.7 mm in images of 400 × 2048 pixels with a lateral resolution of 30 μm and axial resolution of 7 μm, using mid-infrared optical coherence tomography (MIR OCT) based on a 4 μm center wavelength MIR supercontinuum laser. We detected individual printed ceramic layers and tracked predefined defects through all four processing steps and demonstrated how a defect in the green phase could affect the final product. This research sets the stage for NDI integration in AM.